Montepulciano is very charming / rewards time spent there, so I'd call it a good choice. It may be something of a challenge to get a sunny apartment in Montepulciano itself, as the buildings have some age on them and typically designed to dissipate heat in summer, rather than letting the sun in. It's a pleasant place to stroll around, with good views, some good restaurants, a historic cafe that somewhat disappointed (except for the excellent 'mignon' biscuits and cakes), and it's not too large either.
Politian Apartments were very well kept, with modern equipped bathrooms / kitchens, albeit with proper character in the other rooms... but are they still going? They've certainly been a favourite in this group.
It might also be worth a look at agriturismo.it for a farmstay, which is likely to be more modern (or modern refit), and where there is space to grab some sun. This also makes venturing out and about in Tuscany easier, but may compromise enjoying Montepulciano itself, as parking and walking up might get irritating.
What time of year are you going? If July/August I'd be tempted to suggest staying outside, but if April/May/October, to stay in Montepulciano itself
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Now I'm going to throw a couple of major curveballs into your thoughts - different locations outside of Tuscany, but where sunny, updated/modern/clean would fit perfectly.
Massimago in Mezzane di Sotto 20-30 minute drive outside of Verona and also handy for Soave. The apartments are clean, modern, not especially large (but there might also be some larger ones). However the ground, with swimming pool and sauna, fruit trees, vines, grass lounging areas, plus a huge spread for breakfast, made it feel rather fancy yet relaxing. It's also a working (valpolicella/amarone) winery and the wines are good.
Agriurismo val di spinso in Santa Vittoria d'alba, not far from alba/bra. The apartments are large, modern and well-equipped, and spotlessly clean. The grounds charming, with trees for shade, plus a swimming pool and patio bbq area. It's super handy to explore Alba and the fancy wine regions of Barolo and Barbaresco, plus you're at the heart of the Slow Food movement (founded in Bra, with its University in nearby Pollenza). The food is very good in this area.
